1. Field of the Invention
The present invention relates to an organic light emitting device and a display using the same.
2. Discussion of the Related Art
A structural element of an organic light emitting device (organic light emitting diode; OLED) operates based on the principle of electroluminescence. Electrons and holes are injected into a semiconductor material so that they recombine and become electrically neutral. Excited molecules derived from, for example, polyflourenes, generate light when they transit back to the base state. Various known organic compounds for OLEDs may be classified into small molecular weight compounds (SM-OLEDs) and polymeric organic compounds (pLEDs).
Various phenomena, for example, electron conduction (electron transport), hole conduction, and light emission, are involved in the operational efficiency of the OLED, which is defined as the ratio of the amount of emitted light to injected charge carriers. Most materials used in OLEDs are responsible for one of the phenomena, i.e., electron conduction, hole conduction, and light emission. Use of multi-layered structural elements, which are combined together, has been suggested for higher efficiency. In this structure, one layer plays may play a prominent part in conducting holes while another layer in conducting electrons. These multiple layers may be arranged in a predetermined manner for an OLED with higher energy efficiency. Methods of arranging specific material layers for a higher OLED are disclosed in various references.
U.S. Pat. No. 4,885,211 discloses an increase in the efficiency of an SM-OLED by improved injection of electrons into a cathode. In a similar approach, use of a metal having a minor outlet work for the cathode is suggested in Appl. Phys. Lett., 1991, 58, 1992 (Heger et al.).
U.S. Pat. No. 5,061,569 discloses an increase in the efficiency of an SM-OLED by improved injection and conduction of holes. A specific layer made of tertiary amines is used to lower energy barriers between structural elements of the OLED, thus improving hole injection and conduction.
WO 2003001569 A2 (Princeton University) discloses an OLED with a structure including an anode, a polymeric hole transport layer and emissive layer, a low molecular weight exiton blocking layer, a low molecular weight electron-conducting layer, and a cathode. Polyvinylkarbazol (PVK) is used as a hole conductor in the OLED. To obtain a full color display, the PVK layer is doped with luminescent coloring materials to define green, red, and blue spectrum areas thereon. Furthermore, an exiton blocking layer made of a low molecular weight material is disposed between the PVK layer and the cathode.
Although the efficiency of the structural layers of the OLED may be improved, the OLED may require a high energy input for a predetermined level of brightness, and it may have a short life span due to poor durability.